Encyclopedia of Environmental Science and Engineering, Volume I and II

220 DESALINATION

process but also the proper operation of the plant and the

pretreatment needs of the desalination process. Reclamation

of waste waters can be more efficient by combining desali-

nation methods, i.e., electrodialysis and reverse osmosis,

electrodialysis-distillation etc., depending on the raw water

and the specifications.

Desalting processes are more expensive than conven-

tional methods for purification of wastes but they provide

the specific requirements for recycling. The recycling of the

waste waters eliminates also the disposal of these waters,

even partly purified, to already polluted streams, especially

in land regions where the disposal can be limited by concen-

tration and element content.

CONCLUSIONS

Fresh water, Man’s greatest necessity, becomes more scarce

every day, especially in certain places around the world, and

this scarcity limits industry, agriculture and exploitation of

various resources directly necessary for mankind and affects

our lives in many ways.

Desalting processes, on the other hand, can provide

freshwater in large quantities when and where it is needed.

Nevertheless, desalinated water is an industrial product

having higher cost than natural water resources, as all com-

mercial products. Approximately 50% of fresh water costs

are made up of variable charges, principally plant cost.

F = fresh water

brine

brine

brine

brine

brine

feed

water

feed

water

B

D

hollow fiber membrane

membrane

support resin

feed water

fresh

water

fresh water

fresh

water

membrane

support sheet

membrane

support sheet

fresh

water

saline water

feed

pressure tube

A

C F

FIGURE 20 Reverse osmosis hollow fiber module, A. Millions of fiber loops, like hairpins, have both ends encapsuled

in an epoxy tube sheet or short cylinder enclosed in the flanfed water end on right. Magnified section of the end of these

threaded-fine fibers is indicated in B. C is a magnified hollow fiber and D its cross section. The saline water passes on

the shell side from the feed at the left end to reject off the concentrated brine on the right. The permeate of fresh water

discharges from the center of the hollow fiber, D, and from the center of the module A.

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